This invention relates to a subassembly electrical isolation connector for interconnecting adjacent tubular drill rods of a drilling system used in drilling bore holes in earth formations. More particularly, improvements are provided in such connector systems for enhancing the sealing system and for increasing the interior diameter of the subassembly connector.
There is a continuing demand to enhance the functioning of the electrical components and mechanical components associated with the transmission of electromagnetic signals from a location at great depths in the earth to the earth""s surface. Such communication is used in various types of drilling operations, such as measuring while drilling (MWD) and/or logging while drilling (LWD). Other situations, which warrant communication with the earth surface, is during the inspection and evaluation of bore holes. Such communication is particularly important when carrying out directional drilling such as under river beds, subways, unusual earth formations and tapping oil reservoirs. It is important at all times to know precisely the location of the drill bit. A significant effort has been made to develop electrical instruments which are capable of transmitting signals at the drill face or inspection face back to the earth""s surface. Some systems involve the use of the lower portion of the drill string as an antenna for purposes of transmitting via electromagnetic waves, information to the earth""s surface, such as described in U.S. Pat. No. 5,394,141. Such system does not involve the use of an isolation subassembly in the drill string.
Various types of devices which are mounted on the outside of the drill string for monitoring surrounding conditions and/or used in communication are described, for example, in U.S. Pat. No. 4,684,946 to Geoservices and U.S. Pat. No. 5,467,832 to Schlumberger Technology Corporation. The problem with mounting communication devices and sensing devices on the exterior of the drill string is that, particularly with directional drilling, the exterior devices are damaged by striking the formations about the bore hole.
In order to enhance communication with the earth""s surface, it is preferred to electrically isolate drill string components so that electromagnetic signals can be developed for data telemetry. This is achieved by a subassembly connector which electrically isolates adjacent drill string components so that the isolated components provide the two terminals of an antenna to which an alternating current is applied in developing the electromagnetic signal for transmission to the earth""s surface. Examples of such connectors are described in U.S. Pat. No. 5,138,313 to Haliburton Company; U.S. Pat. No. 5,163,714 to Geoservice and Canadian patent application 2,151,525 to McAllister Petroleum Services, Ltd. The various types of subassemblies provide for electrical isolation which are particularly useful in bore hole inspection, but may be subject to failure when used, for example, in directional drilling. It has been found that the drill string, and in particular the subassembly connector, is subjected to extreme torsion compression, tension, and bending moments during directional drilling. Such extreme forces can result in connector failure, usually at the weakest point in the subassembly. The connectors of these patents and patent application may fail due to overstressing and possibly break up at their weakest point. The connectors may even fail to the extent, particularly those of the U.S. patents, that retrieval of the drill bit and other components below the subassembly cannot be achieved.
Various types of outer sleeves are provided for subassembly connections such as described in the aforementioned U.S. Pat. No. 5,138,313. The outer sleeve is a machined component which is threaded to other components of the subassembly to provide an outer member. In order to transmit the torque through the connector, a hexagonal gap block is provided.
Other sleeve arrangements are described in U.S. Pat. Nos. 4,186,807; 4,496,174 and 5,163,714. The arrangement of U.S. Pat. No. 4,186,807 has an outer sleeve which is threaded onto the balance of the components to form a complete structure. U.S. Pat. No. 4,496,174 correspondingly discloses an outer sleeve which forms part of the structure and is clamped and sealed in place. The torque transmitting of the interengaged sleeves is provided by either a serpentine connection or a lug type connection. U.S. Pat. No. 5,163,714 describes an outer sleeve seal system with interconnected coupling sections.
In accordance with an object of an aspect of this invention, a subassembly electrical isolation connector is provided which has an improved seal mechanism and torque transfer devices which provide for increased interior diameter of the passageway through the connector.
In accordance with an aspect of the invention, a subassembly electrical isolation connector for interconnecting adjacent tubular drill rods of a drilling system used in drilling bore holes in earth formations electrically isolates the interconnected drill rods. The connector comprises a sealing membrane for sealing the insulated gap between a first connector and a second connector of the subassembly. The sealing membrane preferably is in the shape of a sleeve overlapping the insulated gap between the connectors with at least its respective ends secured to the respective connector to energize the seal, such that the pressure of the drilling mud ensures seal integrity.
In accordance with another aspect of the invention, in a subassembly electrical isolation connector for interconnecting sections of a tubular drill rod, the subassembly has an electrically insulated connector for and between spaced-apart connector sections to transmit drilling forces therethrough,
the use of a sealing membrane for sealing an insulated spacing in electrically insulated connector to prevent ingress of pressurized drilling mud into the connector and shorting out the spaced apart sections of the connector, the sealing membrane overlapping the connector sections as a continuous sleeve and having at least its sleeve ends sealed to respective portions of the connector sections to activate thereby the sealing membrane.
In accordance with a further aspect of the invention, in a sub assembly electrical isolation connector for interconnecting sections for a tubular drill rod, an electrically insulated connector for and between spaced-apart connector sections,
the connector comprises spaced-apart interfitting components provided on the spaced-apart connector sections and electrically insulating force transmitting components provided between and determining spacing of the spaced apart sections,
electrically insulating force transmitting components provided between and determining spacing between the spaced-apart sections, and
an electrically insulative material injected into a space defined between the spaced-apart sections.